This application is related to and claims priority from Japanese Patent Applications No. 2002-198884 filed on Jul. 8, 2002 and No. 2002-200009 filed on Jul. 9, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an ejector cycle with a refrigerant passage through which refrigerant including a lubrication oil is circulated directly by pumping operation of a compressor from an evaporator to a suction side of the compressor while bypassing at least a nozzle of an ejector.
2. Description of Related Art
Generally, as a vapor compression refrigerant cycle, an ejector cycle, an expansion-valve cycle or the like is used. In the expansion-valve cycle, refrigerant is decompressed by a decompression device such as an expansion valve in is enthalpic, and refrigerant decompressed in the decompression device flows into an evaporator. That is, in the expansion-valve cycle, refrigerant is circulated from a compressor to the compressor through a radiator, the expansion valve and the evaporator in this order, as a single refrigerant circuit. Therefore, refrigerant flowing into the evaporator can be directly sucked into the compressor.
On the other hand, in the ejector cycle, an ejector sucks refrigerant evaporated in an evaporator while decompressing and expanding refrigerant in a nozzle, and increases pressure of refrigerant to be sucked into a compressor by converting expansion energy to pressure energy. For example, in the ejector cycle described in JP-A-5-149652, the refrigerant from the ejector flows into a gas-liquid separator, and is separated into gas refrigerant and liquid refrigerant in the gas-liquid separator. Then, the liquid refrigerant separated in the gas-liquid separator is supplied to the evaporator, and the gas refrigerant separated in the gas-liquid separator is sucked into the compressor. However, in the ejector cycle, refrigerant is circulated from the compressor to the compressor through a radiator, the ejector and the gas-liquid separator in this order as a refrigerant flow (i.e., drive flow), and is circulated from the gas-liquid separator to the gas-liquid separator through the evaporator and the ejector in this order as the other refrigerant flow (i.e., suction flow). Therefore, refrigerant is circulated directly by the compressor in the drive flow, while refrigerant is circulated by a pumping function of the ejector. Thus, if the pumping function of the ejector reduces, a flow amount of the suction refrigerant from the evaporator to the ejector is reduced, and a lubrication oil mixed into refrigerant stays in the evaporator. Accordingly, in this case, heat absorbing performance of the evaporator is reduced, and an amount of lubrication oil returned to the compressor is reduced, thereby reducing lubricating efficiency of the compressor.
Further, in the ejector cycle, the gas-liquid separator stores liquid refrigerant to be supplied to the evaporator and the oil to be returned to the compressor. Because it is necessary to store a large amount of the liquid refrigerant and a large amount of the lubrication oil in the gas-liquid separator, the size of the gas-liquid separator is increased.
In view of the above-described problems of the present invention, it is an object of the present invention to provide an ejector cycle capable of preventing a large amount of a lubrication oil from staying in a low-pressure heat exchanger (i.e., evaporator).
It is an another object of the present invention to provide an ejector cycle that effectively reduces the size of a gas-liquid separator.
It is a further another object of the present invention to provide an ejector cycle that can reduces the lubrication oil staying in the low-pressure heat exchanger while reducing the size of the gas-liquid separator.
According to a first aspect of the present invention, an ejector cycle having an ejector includes a pipe member defining a refrigerant passage through which a refrigerant outlet side of a low-pressure heat exchanger is coupled to a refrigerant suction side of a compressor, and a switching means provided in the refrigerant passage to open and close the refrigerant passage. In the ejector cycle, when the switching means opens the refrigerant passage, at least refrigerant in the low-pressure heat exchanger is introduced to the refrigerant suction side of the compressor directly by the pumping operation of the compressor while bypassing the ejector. Accordingly, a lubrication oil amount staying in the low-pressure heat exchanger can be controlled equal to or smaller than a predetermined amount by introducing the refrigerant including the lubrication oil to the compressor through the refrigerant passage. Therefore, a sufficient amount of the lubrication oil can be returned to the compressor.
Further, the ejector cycle includes a gas-liquid separator for separating refrigerant from the ejector into gas refrigerant and liquid refrigerant, and the gas-liquid separator is disposed such that a gas refrigerant outlet of the gas-liquid separator is connected to the refrigerant suction side and a liquid refrigerant outlet is connected to a refrigerant inlet side of the low-pressure heat exchanger. In this case, the refrigerant including the lubrication oil can be directly introduced to the refrigerant suction side of the compressor by the operation of the compressor when an amount of the lubrication oil staying in the low-pressure heat exchanger is larger than a predetermined value. Therefore, the gas-liquid separator is not required to store a large amount of liquid refrigerant and a large amount of lubrication oil in the ejector cycle. Thus, the size of the gas-liquid separator can be reduced.
Specifically, in a normal operation mode where the switching means closes the refrigerant passage, the refrigerant in the low-pressure heat exchanger is sucked into the ejector by the high-speed refrigerant steam jetted from the nozzle. On the other hand, in an oil return mode (bypass mode) where the switching means opens the refrigerant passage, lubrication oil staying in the low-pressure heat exchanger is introduced directly by the pumping operation of the compressor to the compressor, together with the refrigerant flowing from the low-pressure heat exchanger to the refrigerant suction side of the compressor through the refrigerant passage.
For example, the switching means is disposed to open the refrigerant passage, when a refrigerant pressure at the refrigerant outlet side of the low-pressure heat exchanger becomes higher than a refrigerant pressure at the refrigerant suction side of the compressor, and when a pressure different between the refrigerant pressure at the refrigerant outlet side of the low-pressure heat exchanger and the refrigerant pressure at the refrigerant suction side of the compressor is larger than a predetermined value. Alternatively, the switching means is disposed to open the refrigerant passage when an ejector efficiency of the ejector becomes lower than a first predetermined value, and to close the refrigerant passage when the ejector efficiency of the ejector becomes higher than a second predetermined value. In this case, the first predetermined value can be equal to the second predetermined value, or can be different from the second predetermined value.
According to a second aspect of the present invention, in an ejector cycle having the ejector, a pipe member defining a refrigerant passage is provided such that refrigerant discharged from the compressor is introduced through the refrigerant passage toward the low-pressure heat exchanger while bypassing the nozzle of the ejector, and a switching means is provided in the refrigerant passage to open and close the refrigerant passage. In the ejector cycle, when the switching means opens the refrigerant passage, at least refrigerant in a low-pressure heat exchanger is introduced to the refrigerant suction side of the compressor while bypassing the nozzle of the ejector. Therefore, lubrication oil staying in the evaporator can be effectively introduced to the compressor by operation of the compressor. Specifically, a decompression device is disposed in the refrigerant passage for decompressing refrigerant discharged from the compressor. In this case, in the normal operation mode, the switching means closes the refrigerant passage, and the high-pressure refrigerant from the high-pressure heat exchanger is decompressed in the nozzle of the ejector while sucking refrigerant in the evaporator. On the other hand, in the oil return mode (bypass mode), the switching means opens the refrigerant passage, and the high-pressure refrigerant discharged from the compressor is decompressed in the decompression device and flows through the low-pressure heat exchanger. Therefore, in the oil return mode, the amount of the lubrication oil staying in the low-pressure heat exchanger can be effectively reduced.